British Patent Number GB2340917 describes a rotary gate valve comprising a housing that supports a valve seat and valve gate. The valve seat has an inlet port and an outlet port, and fluid communication therebetween is controlled by the valve gate. The valve gate is angularly moveable between a closed position in which it seals at least one of the inlet and outlet ports, and an open position in which fluid can communicate between the inlet and outlet ports, via the valve gate. A contacting face of the valve gate is maintained in sliding contact with the valve seat throughout the range of movement (from closed to open positions), and the contacting face of the valve gate forms a metal to metal seal with the valve seat in the closed position. In some arrangements, the valve gate includes at least one gate button, each of which comprise a circular contacting face. Each gate button has a circular cross section, and the circular contacting face is larger in diameter than the circular port of the valve seat that is sealed thereby in the closed position. The gate buttons are spring biased into engagement with, and so exert a load on, the valve seat. In the fully closed position, the circular contacting face of the gate button is concentric with the circular port that it seals.
In use, when the valve gate is moved to an opened position, the buttons no longer close the inlet and outlet ports, and fluid is able to flow between the inlet and outlet ports via flow passages provided in the valve gate and a chamber located to the opposition side of the valve gate to the inlet and outlet ports.
It will be appreciated that the initial fluid flow upon cracking open of the valve occurs through only a small cross sectional area. During this phase of the operation of the valve, the gate buttons are only supported about part of the periphery thereof. The combination of the fluid flow and the applied fluid pressures, especially where the valve is being used to control the flow of fluids under high pressure, for example in the region of 15000 psi, may tend to result in limited deflection or tilting of the buttons which, in turn, may damage a wear resistant coating applied to the valve seat, for example causing cracking thereof. Obviously, this is undesirable.
One of the objects of the present invention, therefore, is to relieve this problem.